Canyon gate transistor and methods for its fabrication

ABSTRACT

Lithographic limitations on gate and induced channel length in MOSFETS are avoided by forming non-planar MOSFETS in a cavity extending into a semiconductor substrate. The gate insulator and channel region lie proximate a cavity sidewall having angle α preferably about ≧90 degrees with respect to the semiconductor surface. The channel length depends on the bottom depth of the cavity and the depth from the surface of a source or drain region adjacent the cavity. The corresponding drain or source lies at the cavity bottom. The cavity sidewall extends therebetween. Neither depth is lithographic dependent. Very short channels can be consistently formed, providing improved performance and manufacturing yield. Source, drain and gate connections are brought to the same surface so that complex circuits can be readily constructed. The source and drain regions are preferably formed epitaxially and strain inducing materials can be used therein to improve channel carrier mobility.

FIELD OF THE INVENTION

This invention relates generally to structures and methods for formingsemiconductor devices, especially non-planar field effect transistors(FETs).

BACKGROUND OF THE INVENTION

In the field of electronics, the planar metal-oxide-semiconductor (MOS)field effect transistor (FET) is widely used. In planar devices, theconductive channel that gives rise to device operation liesapproximately parallel to the semiconductor surface on or in which theplanar MOSFET is formed. As the fabrication technology has improved,there has been an ongoing effort to shrink the dimensions of theindividual MOSFETs so that denser and more complex integrated circuits(ICs) can be fabricated. With the planar MOSFET, the gate length andcorresponding induced source-drain channel length or spacing anduniformity are largely controlled by lithographic capabilities, forexample, the lithographic images used to define the MOSFET gate and/orsource-drain channel length. Unfortunately, lithography is rapidlyapproaching fundamental physical limitations so that it becomes more andmore difficult to consistently and uniformly define small images anddevice elements such as the gate and source-drain channel length.

More recently, MOSFETs have been developed in which the field inducedconductive channel is no longer limited substantially to the plane ofthe semiconductor surface, but extends into other dimensions. Fin-typeFETs and trench-FETs are examples of such non-planar FETs. However,these non-planar FETs have limitations and problems of their own and sothere is an ongoing need for further device structures and methodswherein the gate length and induced source-drain channel lengths of theMOSFETs are not dependent on lithographic capabilities or limitationsbut can be determined by other means independent of such lithographiclimitations and which can still be fabricated using available processingcapabilities.

BRIEF SUMMARY OF THE INVENTION

Lithographic limitations on gate and induced channel length in MOSFETSare avoided by forming non-planar MOSFETS (20, 20′, 80, 80′) in cavities(50) extending into a semiconductor substrate (21). The gate insulator(26, 96) and channel region (29, 29′) lie proximate a cavity sidewall(27). The cavity sidewall (27) has an angle α with respect to thesemiconductor surface (212) where α is desirably at least about 90degrees and may be as much as or more than about 95 degrees. The channellength (30) depends on the bottom depth (51) of the cavity and the depth(241, 641) from the surface (212) of a source or drain region (24, 64,68) adjacent the sidewall (27) of the cavity (50). The correspondingdrain or source (22, 62) lies at the cavity bottom (52). The cavitysidewall (27) extends therebetween. Neither depth is lithographicallydependent. Very short channels can be consistently formed, providingimproved performance and manufacturing yield. Source, drain and gateconnections (44, 42, 48) are brought to the front surface (212) so thatcomplex circuits can be readily constructed. The source and drainregions (22, 62 or 24, 64) are preferably formed epitaxially and straininducing materials can be used therein to improve channel carriermobility and reduce ON-resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the followingdetailed description, taken in conjunction with the accompanying figuresin the drawings in which like numerals denote like or analogouselements, and wherein:

FIG. 1 shows a simplified cross-sectional view and FIG. 2 shows asimplified plan view of a MOSFET having a non-planar channelconfiguration, according to an embodiment of the invention;

FIG. 3 shows a simplified plan view of a MOSFET analogous to that ofFIG. 2, but according to another embodiment of the invention;

FIGS. 4-12 show simplified cross-sectional views of the MOSFET of FIGS.1-2 (and 3) during various stages of manufacture, according to furtherembodiments of the invention;

FIGS. 13-18 show simplified cross-sectional views of the MOSFET of FIGS.1-2 (and 3) during various stages of manufacture, according to stillfurther embodiments of the invention; and

FIGS. 19-27 show simplified cross-sectional views of the MOSFET of FIGS.1-2 (and 3) during various stages of manufacture, according to still yetfurther embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, or the following detailed description. For simplicity andclarity of illustration, the drawing figures illustrate the generalmanner of construction, and descriptions and details of well-knownfeatures and techniques may be omitted to avoid unnecessarily obscuringthe invention. Additionally, elements in the drawings figures are notnecessarily drawn to scale. For example, the dimensions of some of theelements or regions in the figures may be exaggerated relative to otherelements or regions to help improve understanding of embodiments of theinvention.

The terms “comprise,” “include,” “have” and any variations thereof, areintended to cover non-exclusive inclusions, such that a process, method,article, or apparatus that comprises a list of elements or steps is notnecessarily limited to those elements or steps, but may include otherelements or steps not expressly listed or inherent in such process,method, article, or apparatus. The term “coupled,” as used herein, isdefined as directly or indirectly connected in an electrical ornon-electrical manner. As used herein the terms “substantial” and“substantially” mean sufficient to accomplish the stated purpose in apractical manner and that minor imperfections, if any, are notsignificant for the stated purpose. Furthermore, the terms “first,”“second,” “third,” “fourth” and the like in the description and theclaims, if any, may be used for distinguishing between somewhat similarelements and not necessarily for describing a particular spatialarrangement or sequence or chronological order. It is to be understoodthat the terms so used are interchangeable under appropriatecircumstances such that the embodiments of the invention describedherein are, for example, capable of operation or construction insequences, orientations and arrangements other than those illustrated orotherwise described herein.

Metal-oxide-semiconductor (MOS) devices are a well known form of fieldeffect transistors (FETs) and can be fabricated as either P-channel(PMOS) or N-channel (NMOS) devices. Complimentarymetal-oxide-semiconductor (CMOS) devices include both PMOS and NMOSdevices and are much used in integrated circuits (ICs). The termmetal-oxide-semiconductor and the abbreviation (MOS) are widely used inthe art to refer to insulated gate field effect transistors or devices(IGFETs) irrespective of whether they employ metals or some other formof conductor for the gates of such devices, and irrespective of whetherthey use oxide for the gate insulator or some other form of dielectricfor the gate insulator. Doped semiconductors, metal-semiconductoralloys, semi-metals and combinations thereof are non-limiting examplesof suitable gate conductors. Oxides, nitrides, fluorides, combinationsthereof and other inorganic and organic dielectrics are non-limitingexamples of suitable gate insulators. Accordingly, the termmetal-oxide-semiconductor and the abbreviations MOS, MOSFET, PMOS, NMOSand CMOS as used herein are intended to refer broadly to such insulatedgate field effect transistors or devices (IGFETs) and not be limitedmerely to those employing just metal as the gate conductor and/or justoxide as the gate insulator.

For convenience of explanation, embodiments of the invention aredescribed herein for MOSFETs employing silicon semiconductors (SC).However, persons of skill in the art will understand that suchembodiments are not limited merely to silicon (Si) semiconductors (SC),but also apply to other SC materials and other types of SC devices.Further, as used herein, the term “semiconductor”, singular or plural,and the abbreviation “SC” therefore, are intended to include any kind ofsemiconductor material, including but not limited to single crystalsemiconductors, polycrystalline semiconductors, amorphous semiconductorsas well as organic and inorganic semiconductors. As used herein, theterm “substrate”, singular or plural, is intended to include bulksemiconductor substrates, insulating substrates, and combinationsthereof such as but not intended to be limiting,semiconductor-on-insulator (SOI) substrates andinsulator-on-semiconductor (IOS) substrates. Substrates may be singlecrystal, polycrystalline, amorphous, laminated or combinations thereof.For convenience of description, various conductors may be referred to as“metals”, but unless indicated otherwise by the particular context, thewords “metal” and “conductor”, singular or plural, should be interpretedbroadly to include any type of electrical conductor, whether metallic ornot. Semiconductors, doped semiconductors, metals, semi-metals, metalalloys, semiconductor-metal alloys and combinations thereof arenon-limiting examples of useful electrical conductors. The abbreviation“SC” is used herein for the terms “semiconductor” and “semiconductormaterial”.

FIG. 1 shows a simplified cross-sectional view and FIG. 2 shows asimplified plan view of MOSFET 20 having a non-planar channelconfiguration, according to an embodiment of the invention. In FIG. 2(and FIG. 3), overlying regions are assumed to be transparent so thattheir lateral extent and relative location may be easily seen. FIGS. 1and 2 are discussed together. While MOSFET 20 is shown in the plan viewof FIG. 2 as having an annular shape, this is merely intended toillustrate a preferred embodiment, and other non-annular arrangementsmay also be used and are intended to be included herein.

MOSFET 20 is formed in semiconductor (SC) substrate 21 of a firstconductivity type, e.g., N or P, in which are located source and drainregions 22, 24 of a second, opposite conductivity type, e.g., P or N.Substrate 21 has upper or front surface 212. Persons of skill in the artwill understand that either of regions 22, 24 may serve as the “source”of MOSFET 20 and the other serve as the “drain” of MOSFET 20, and whileone region may be referred to herein as the “source” and the other asthe “drain” at various times, this is not intended to imply that theparticular region referred to must always be used for such purpose.Accordingly, while region 22 (and subsequently described region 62) maybe referred to in some locations herein as acting as the source ofMOSFET 20 and region 24 (and subsequently described region 64) may bereferred to as acting as the drain of MOSFET 20, in other locationsherein such designations may be interchanged so that region 22 (andregion 62) is identified as the drain and region 24 (and region 64) asthe source. This is indicative of the dual functionality of dopedregions 22, 24 (and regions 62, 64 subsequently described) and the exactchoice of function will depend upon the particular circuit beingimplemented by the user.

In MOSFET 20 of FIGS. 1-2, drain 24 with alloy contact region 25 liessubstantially adjacent to surface 212 and source 22 with alloy contactregion 23 is located beneath surface 212 within substrate 21. Source 22and drain 24 are vertically separated by distance 30. Sidewall 27 ofsubstrate 21 extends between source 22 and drain 24. Located on sidewall27 is gate dielectric 26, one side of which is in contact with sidewall27 and the other side of which is in contact with gate conductor 28. Inplan view, gate conductor 28 of FIGS. 1-2 has a generally annular shape,that is, with an internal lateral opening of width 331 surrounded byannular gate conductor 28 of annular width 281. In the example of FIGS.2, MOSFET 20 has an approximately rectangular shape, but this is notintended to be limiting, and other plan view shapes (e.g. and notintended to be limiting, polygonal, circular, elliptical, etc.) may alsobe used, and such annular shape, if used, need not be closed. Theinversion channel length L (or stated another way, the “gate length” L)of MOSFET 20, corresponds substantially to distance 30.

When gate conductor 28 is appropriately biased, a conductive inversionchannel indicated by arrow 29 forms between source (or drain) 22 anddrain (or source) 24, more specifically between region 222 of source (ordrain) 22 and region 242 of drain (or source) 24 proximate sidewall 27.For convenience, arrow 29 is also referred to herein as inversionchannel 29, since it illustrates the primary current carrying pathbetween doped region 22 (e.g., the source or drain) and doped region 24(e.g., the drain or source) giving rise to the useful properties ofMOSFET 20. The nature of the charge carriers (e.g., electrons or holes)and the direction of current flow in inversion channel 29 will dependupon whether MOSFET 20 is N or P type and the source-drain bias. Source22 is desirably provided with metal-SC alloy contact region 23 and drain24 is desirably provided with metal-SC alloy contact region 25, butother materials making Ohmic contact to source and/or drain regions 22,24 may also be used. Silicides are non-limiting examples of suitablemetal-SC alloy contact materials for silicon semiconductor. Contactregions 23, 25 are desirable but not essential. Dielectric region 33conveniently overlies contact region 23 above source 22, extendingsubstantially to surface 212. Interlayer dielectric 34 desirablyoverlies dielectric region 33 and surface 212 with drain (or source)contact region 25. Passing through interlayer dielectric 34 is: (i)drain (or source) connection 44 electrically coupled to drain (orsource) contact region 25, and (ii) gate connection 48 electricallycoupled to gate 28. Passing through interlayer dielectric 34 anddielectric region 33 is source (or drain) connection 42 electricallycoupled to source (or drain) contact region 23. Further interlayerdielectric regions (not shown) and interconnections (not shown) may beused to couple connections 44, 48, 42 to other devices and power andground leads.

It will be noted that, unlike prior art trench-FETs, all threeterminals, e.g., source, drain and gate connections 42, 44, 48, ofMOSFET 20 are available on front surface 47 of MOSFET 20. In prior artplanar MOSFETs the channel length is generally determined or related tothe lithographically defined gate length that is substantially parallelto the principal surface of the semiconductor substrate in or on whichthe planar device is formed. The greater the lithographic limitationsand lack of consistency, the greater the difficulties of accurately andconsistently defining the channel length in planar MOSFETs. It will benoted that in MOSFET 20 of FIGS. 1-2, the inversion channel (e.g., gate)length L corresponds to depth or distance 30 and, unlike planar MOSFETS,is not dependent on lithographic capabilities or tolerances. As will besubsequently shown in connection with FIGS. 4-27, inversion channel orgate length 30 depends on depth 51 of etched cavity 50 (see FIGS. 4-5)in whose bottom 52 is formed doped (e.g., source) region 22, and depth241′, 241 (see FIGS. 5 and 11-12) to which doped (e.g., drain) region 24extends beneath surface 212 of substrate 21. (In FIG. 27 channel length30′ also depends on the depth of further doped region 68.) Cavity etchdepth 51 (see FIGS. 4-5) and depth 241′, 241 (see FIGS. 5 and 11-12) ofdoped region 24 are relatively precisely controllable process parametersunrelated to lithographic definition and repeatability, thereby enablingone to consistently and accurately select and obtain predetermineddistance 30 for inversion channel or gate length L of substantiallyvertical MOSFET 20 without being dependent upon lithographiccapabilities or consistency. This is a significant advance in the artand highly desirable. Further, having source, drain and gate terminals42, 44, 48 of MOSFET 20 available on front surface 47 of MOSFET 20 makesit possible to form large, complex and dense integrated circuits (ICs)using available processing technology. This is a very valuablecapability of great commercial significance.

FIG. 3 shows a simplified plan view of MOSFET 20′ analogous to that ofMOSFET 20 of FIG. 2, but according to another embodiment of theinvention. MOSFET 20′ has source-drain regions 22, 24, contact regions23, 25, gate conductor 28′, sidewall 27, central dielectric region 33′and connections 42′, 44′, 48′ that are analogous to regions 22, 23, 24,25, 28, 27, 33, 42, 44, 48 of FIGS. 1-2 but with somewhat different planview shapes. MOSFET 20′ of FIG. 3 differs from MOSFET 20 of FIG. 2 inthat extension 39 of gate region 28′ is provided, for example on oneside of MOSFET 20′, to allow gate connection 48′ to be providedlaterally outside plan view annular footprint 491-492 of gate 28′.Lateral width 282 of gate extension 39 of MOSFET 20′ of FIG. 3 may bemade wider than annular gate width 281 of device 20 of FIG. 2. Thisfacilitates lithographic placement of gate connection 48′, therebyimproving manufacturing yield. Further, lateral annular width 281′ ofgate 28′ may be made smaller, thereby reducing the overlap capacitancebetween gate 28′ and source (or drain) region 22, thereby improvingdevice performance in certain circumstances. In addition, forsubstantially similar outer perimeter of gate 28′, reducing annular gatewidth 281′ increases width 331′ of central dielectric region 33′ throughwhich connection 42′ to source (or drain) contact region 23 convenientlypasses. Source (or drain) connection 42′ may now be made larger, as candrain (or source) connection 44′ that lies laterally outside of gate28′. This reduces the series source-drain connection ON resistance andincreases the drive current capability of the device 20′. Thesedesirable advantages are realized in MOSFET 20′ of FIG. 3 by placinggate connection 48′ laterally outside of substantially annular gatefootprint 491-492.

FIGS. 4-12 show simplified cross-sectional views of MOSFET 20 of FIG.1-2 during various stages 504-512 of manufacture, according to furtherembodiments of the invention. Persons of skill in the art willunderstand that these same manufacturing stages also substantially applyto MOSFET 20′ of FIG. 3 taking into account the differences in lateralsizes and locations of the various regions being formed. FIG. 4-12 areintended to illustrate by way of example and not limitation, a basicmanufacturing process for forming device 20, 20′ of FIGS. 1-3, butpersons of skill in the art will understand that many variations arepossible, which variations are intended to be included.

Referring now to manufacturing stage 504 of FIG. 4, substrate 21 isprovided having thickness 210 and upper surface 212. Substrate 21 may bemonolithic or layered and amorphous or single crystal or combinationsthereof, provided that sidewall 27 of substrate 21 includes asemiconductor in which induced channel 29 of FIGS. 1, 12 and 18 andchannel 29′ of FIG. 27 may be formed. By way of example and not intendedto be limiting, for an NMOS device, substrate 21 adjacent or aroundsidewall 27 is conveniently P-type with a doping density in the range ofabout 10E16 to 10E18 cm⁻³, and for a PMOS device, substrate 21 adjacentor around sidewall 27 is conveniently N-type with a doping density inthe range of about 10E16 to 10E18 cm⁻³, but other substrates and dopingdensities may also be used. Thickness 210 will depend primarily on thelateral size of substrate 21 and the choice thereof is within thecompetence of those of skill in the art. Mask 40 having closed portions401 and open portion 402 is provided on surface 212.

Cavity 50 having sidewall 27 and bottom 52 at depth 51 from surface 212is etched or otherwise excavated into substrate 21 beneath open portion402 of mask 40. Cavity 50 is preferably created usingreactive-ion-etching (RIE). RIE conveniently provides sufficient etchanisotropy to form the illustrated cavity profile with angle α desirablyin the range of about 90-95 degrees, preferably about 90 degrees. Cavitydepth 51 can be controlled during etching by an opticalintereferometrical measurement. This is a well known technique in theRIE art. By way of example and not intended to be limiting, depth 51 isusefully in the range of about 10 to 50 nanometers, but larger orsmaller depths may also be used. Structure 604 results. The lateralperimeter of cavity 50 in plan view substantially determines theperimeter of gate 28 of device 20 and can be selected by those of skillin the art depending upon the desired device properties. In the contextof standard planar MOSFET terminology, the outer lateral perimeter ofcavity 50 corresponds approximately to the gate or channel “width” asthat term is used for planar MOSFETs.

Sidewall 27, adjacent to which conductive channel 29 (see FIG. 1) willbe induced during operation of device 20, makes angle α with surface 212of substrate 21. While the various embodiments illustrated here areshown as having substantially vertical sidewalls 27, that is with α˜90degrees and proceeding relatively straight toward bottom 52, this ismerely intended to illustrate a preferred embodiment and not intended tobe limiting. Accordingly, as used herein, the term “non-planar” withrespect to MOSFETs is intended to include any device wherein angle α isequal to or greater than about 90 degrees. Sidewall 27 may be curved orsubstantially straight. Having angle α≧90 degrees is useful in avoidingundesired doping of sidewall 27 during manufacturing stage 505 of FIG.5.

Referring now to manufacturing stage 505 of FIG. 5, mask 40 is removedand Implant A provided wherein dopant of the desired type and dose isimplanted to depth 241′ into portions 213 of substrate 21 laterallyoutside of cavity 50 to form doped region 24′, and to depth 221′ inportion 214 of substrate 21 beneath bottom surface 52 of cavity 50 toform doped region 22′. Doped region 24′ is the precursor to doped region24 and doped region 22′ is the precursor to doped region 22 of FIGS.1-3. Initial depth 241′ of initial doped region 24′ is the precursor tofinal depth 241 of final region 24 of FIGS. 1 and 12. It will beunderstood by those of skill in the art that some out-diffusion of theimpurities of initial regions 22′, 24′ will occur as a result of thevarious thermal processes to which device 20 is subjected duringsubsequent manufacturing stages. Persons of skill in the art willunderstand how to take such out-diffusion into account in selectinginitial doping depth 241′ in order to reach a predetermined final dopingdepth 241 in the finished device illustrated in FIGS. 1 and 12.Ordinarily, depths 241′ and 221′ are substantially the same but this isnot essential and in other embodiments, different doping depths 241′,221′ (and 241, 221) may be used. While ion implantation is a preferredmeans of forming initial doped regions 22′, 24′ (and resulting dopedregions 22, 24), it is indicated by way of a preferred example and notlimitation and other doping procedures well known in the art may also beemployed. The implant dose and energy associated with Implant A shouldbe chosen so as to provide the desired doping density and depth ofregions 22′, 24′ and 22, 24 that serve as the source-drain (ordrain-source) regions of device 20. This is within the competence ofthose of skill in the art, but in general the doping density isdesirably about 10¹ to 10³ time the doping density of substrate 21proximate sidewall 27, but higher or lower doping densities may also beused. Structure 605 results. If undesired doping of sidewall 27 hasoccurred during manufacturing stage 505, then a brief isotropic etch maybe used to remove such undesired doping from sidewall 27.

Referring now to manufacturing stage 506 of FIG. 6, at least surfaces 27and 52 are provided with dielectric layer 26′, of which portion 26 ofthickness 261 on sidewall surfaces 27 can, in this example, subsequentlyserve as the gate dielectric or gate insulator, and portion 26″ ofdielectric layer 26′ conveniently but not essentially extends oversurface 212 of substrate 21. SiO₂, SiON, HFO₂, HFSiO₂, ZrO₂ andcombination thereof are non-limiting example of useful materials fordielectric layer 26′, but other inorganic or organic insulators may alsobe used. Conductor layer 28″ of thickness 285 is provided over substrate21 and over dielectric layer portions 26, 26′, 26″ and extending intocavity 50. Conductor layer 28″is conveniently of in-situ doped polysilicon or titanium-nitride (TiN), but other conductors such as thosethat have been described above may also be used. TiN is preferred.Thickness 285 is desirably at least equal to depth 51 of cavity 50, butother depths may also be used. Structure 606 results.

Referring now to manufacturing stage 507 of FIG. 7, structure 606 isdesirably planarized using means well known in the art, such as forexample and not intended to be limiting, chemical-mechanical polishing(CMP). CMP for planarization of conductor layers is well known in theart. Planarization is conveniently stopped at surface 212 of substrate21. Structure 607 results in which upper surface 285 of conductor 28″ issubstantially coplanar with surface 212 of substrate 21.

Referring now to manufacturing stage 508 of FIG. 8, mask 45 havingclosed portions 451 and open potion 452 is provided above surfaces 212and 285. The portion of conductor 28″ (see FIG. 7) exposed through openportion 452 is etched away, thereby providing approximately centrallylocated cavity 54 of width 331 in conductor 28″ substantially laterallysurrounded by gate conductor 28 of lateral width 281. Cavity 54 extendsto dielectric region 26′ on bottom 52 of cavity 50. That portion ofdielectric region 26′ underlying cavity 54 is desirably then removed bymeans of a brief dielectric etch, thereby exposing surface portion 521of bottom surface 52 of cavity 50 underlying cavity 54. Structure 608results. While that portion of dielectric layer 26′ underlying cavity 54is conveniently removed at this stage as noted above, that is notessential and it may be removed as a part of subsequent manufacturingstage 509. Either arrangement is useful.

Referring now to manufacturing stage 509 of FIG. 9, mask 45 of structure608 is removed. Surface 212 of portions 213 of substrate 21 and portion214 of substrate 21 underlying bottom surface portion 521 under cavity54, are exposed to a metal adapted to form metal-SC alloy contact region23′ in source (or drain) region 22′ and metal-SC alloy contact region25′ in drain (or source) region 24′. Where substrate is of silicon, thenNickel and Cobalt are non-limiting examples of suitable metals forforming metal-SC alloy contact regions 23′, 25′, where Nickel ispreferred. By way of example and not limitation, in a preferredembodiment, nickel material is blanket sputtered on structure 608 toabout 10 to 15 nm thickness, but thicker and thinner layers may also beused. A brief rapid-thermal-anneal (RTA) is performed at about 280-350degrees Celsius for about 30 seconds, but other temperatures and timesmay also be used. This results in formation of nickel-silicide onlywhere the sputtered nickel overlies silicon. This if referred to as aself-aligned silicide, often abbreviated as “salicide”. A brief wet etchis used to remove any un-reacted nickel, leaving behind themetal-semiconductor (e.g., NiSi) alloy contacts. A further slightlyhigher temperature RTA (e.g., at 400-480 degrees Celsius for about 30seconds) is desirably but not essentially applied to adjust the grainsize of the NiSi alloy contacts. In this way the metal used to formmetal-SC alloy contact regions 23′, 25′ does not significantly depositon the narrow ends of gate dielectric 26 laterally surrounding gateconductor 28 between gate conductor 28 and doped region 24′ at surface212 and in cavity 54 between the bottom of gate 28 and doped region 22′.This is useful since it avoids or minimizes gate-drain and gate-sourceshorts across the exposed narrow ends of gate dielectric 26 adjacentgate conductor 28. Where substrate 21 is of silicon, gate 28 is of TiNand metal-SC alloy contact is of nickel-silicide, then a sulfuric acidhydrogen peroxide mixture is a non-limiting example of a suitable etchfor clearing gate-source and gate-drain shorts that may be associatedwith these narrow gate dielectric edges as a result of alloy contactformation, but other etchants may also be used depending upon theparticular combination of gate and alloy contact conductors chosen bythe user. Annealing to facilitate the formation of the metal-SC alloycontacts 23′, 25′ (and subsequently 23, 25) may be carried outseparately as described above or may be combined with temperature cyclesassociated with dielectric depositions described later, which promotethe formation of the metal-SC alloy and the out-diffusion of the dopantsof initial regions 22′, 24′ as mentioned earlier. In recognitionthereof, the boundaries of regions 24, 25′ are still shown as dashedlines in FIG. 9. Structure 609 results.

Referring now to manufacturing stage 510 of FIG. 10, dielectric layer33′ of, for example and not intended to be limiting, SiO₂ (e.g., madeusing TEOS) is formed over structure 609, preferably but not essentiallyto a thickness at least about equal to cavity depth 51. Structure 610results. Referring now to manufacturing stage 611 of FIG. 11, structure610 is desirably planarized, e.g., using CMP, leaving behind centraldielectric region 33 within substantially annular gate 28, coveringdoped region (e.g., source or drain) 22 with metal-SC alloy contactregion 23′ on bottom portion 521 and extending desirably to surface 212of substrate 21. CMP for planarization of dielectric regions is wellknown in the art. In recognition of the various annealing or otherthermal processing associated with these and preceding operations, dopedregions 22 and 24 are shown as solid lines in FIG. 11 indicating thatsuch out-diffusions as may occur has substantially been completed sothat region 24 has substantially reached its final depth 241 fromsurface 212, and in combination with depth 51 of cavity 50 therebydefined induced channel length 30. The boundaries between metal-SC alloycontact region 23 and source (or drain) region 22 and between metal-SCalloy contact region 25 and drain (or source) region 24 are left asdashed lines, since their precise locations within doped regions 22, 24are not critical. Persons of skill in the art will understand that anysignificant thermal processing associated with formation of anysubsequent interlayer dielectrics and conductive interconnections areeither not significant or can be taken into account as part of theoverall thermal budget that may affect induced channel length 30. Suchthermal budget and out-diffusion calculations are within the competenceof persons of skill in the art. Structure 611 results.

It is desirable but not essential that lateral end 223 of doped region22 extend laterally (e.g., to the left and right) to or beyond sidewall27 so that induced channel current 29 flows substantially parallel tosidewall 27 between portions 222 and 242 of regions 22 and 24. To theextent that region 22 does not extend laterally to or beyond sidewall 27(as for example if end 223 is partially recessed beneath gate 28), theninduced channel current 29 will initially flow substantiallyhorizontally until it reaches the lateral location of sidewall 27 andthen turn upward to flow substantially parallel to sidewall 27 to dopedregion 24. Either arrangement is useful, but having end 223 of dopedregion 22 extend laterally to or beyond sidewall 27 is preferred. FIGS.1-12 have shown sidewall 27 as being substantially vertical andperpendicular to surface 212 of substrate 21 but, as discussed above,this is not essential and sidewall 27 does not have to be straight andsmooth as has been illustrated. Either arrangement is useful.

Structure 611 may be used as is or provided with further overlyingdielectric layers and electrical contacts or interconnections, as iscommon in the art. Referring now to manufacturing stage 512, structure611 has dielectric layer 34 formed thereon, vias corresponding to thedesired locations of electrical connections 42, 48, 44 provided therein(and through dielectric region 33 in the case of conductor 42), whichare then filled with electrical conductors to form electricalconnections to doped (source or drain) region 22, gate 28 and doped(drain or source) region 24, respectively. Structure 612 results.Further dielectric layers and interconnections may also be provideddepending upon the particular device structure or integrated circuitbeing formed.

FIGS. 13-18 show simplified cross-sectional views of MOSFET 80 of FIGS.1-2 during various stages of manufacture 513-518, according to stillfurther embodiments of the invention. Persons of skill in the art willunderstand that these same manufacturing stages apply to the structureshown in FIG. 3 taking into account the differences in lateral sizes andlocations of the various regions being formed. Referring now tomanufacturing stage 513 of FIG. 13, structure 406 of FIG. 4 hasdielectric layer 60 of thickness 701 formed on surfaces 212, 27 and 52,as for example by deposition or growth of SiO₂ or other dielectric usingmeans well known in the art. Silicon oxide is a non-limiting example ofa suitable dielectric material for layer 60, but other materials mayalso be used. In a preferred embodiment, thickness 701 of layer 60 isdesirably in the range of about 1 to 3 nanometers, but thicker orthinner layers may also be used. Overlying layer 60 is layer 61′ ofthickness 702, of for example and not intended to be limiting, siliconnitride, but other materials may also be used. Thickness 702 isdesirably in the range of about 3 to 8 nanometers, but thicker orthinner layers may also be used. It is desirable but not essential thatthe material of layer 61′ be differentially etchable with respect to thematerial of layer 60. Structure 613 results.

Referring now to manufacturing stage 514 of FIG. 14, structure 613 ofFIG. 13 is anisotropically etched to remove layers 61′ and 60 except onsidewall 27 of cavity 50, leaving behind that portion of layer 60 onsidewall 27 covered in turn by portion 61 of the material of layer 61′,collectively referred to as sidewall protector 70 having lateral width71 on bottom 52 of cavity 50. While sidewall protector 70 isconveniently of two materials as described above, it may also be formedfrom any material of combination of materials that is substantiallydifferentially etchable with respect to the material of substrate 21 andsubstantially resistant to reagents that etch the material of substrate21. Either arrangement is useful. Procedures for forming such sidewallprotectors are well known in the art. Surface 212 of substrate 21 andportion 522 of bottom 52 of trench 50 laterally within sidewallprotector 70 are exposed. Structure 614 results.

Referring now to manufacturing stage 515 of FIG. 15, structure 614 ofFIG. 14 is subjected to an isotropic semiconductor etch adapted toremove those portions of substrate 21 in locations 213, 214 not coveredby sidewall protector 70 of manufacturing stage 514. In this mannerportion 64″ of substrate 21 beneath surface 212 in location 213 andportion 62″ of substrate 21 beneath exposed portion 522 of bottom 52 ofcavity 50 in location 214 are removed. Wet chemical etching is anon-limiting example of a suitable isotropic etch procedure for formingcavities 64″, 62″. By controlling lateral thickness 71 of sidewallprotector 70 and use of an isotropic etch of at least depth 73″ intosubstrate 21, lateral end portion 731″ of cavity 62″ can extendlaterally to or beyond sidewall 27. In a preferred embodiment, depth 73″is desirably at least equal to lateral thickness 71 of sidewallprotector 70. Structure 615 results.

Referring now to manufacturing stage 516 of FIG. 16, structure 615 ispreferably subject to in-situ doped selective epitaxial growth ofsemiconductor to fill in cavity 64″ in location 213 and cavity 62″ inlocation 214, thereby creating doped SC region 64 of thickness 641adjacent upper surface 212 in location 213, and doped SC region 62adjacent surface 52 in location 214 having end portion 731 extendinglaterally to or beyond sidewall 27. Where substrate 21 is of silicon,epitaxial growth of doped regions 64, 62 is conveniently carried out bylow pressure chemical vapor deposition (LPCVD), but other well knownepitaxial growth techniques may also be used. Regions 64, 62 areconveniently doped to impurity concentrations in the range of about 1E19to 5E20 cm⁻³, but higher and lower impurity concentrations can also beused. Boron is non-limiting example of suitable impurity for PMOSdevices and phosphorous and Arsenic and combinations thereof arenon-limiting example of suitable impurities for NMOS devices, but otherimpurities may also be used. Doping of epi-regions 62, 64 may be carriedout during epitaxial growth or later. Either arrangement is useful.Doped region 64 of thickness or depth 641 are analogous in function todoped region 24 of thickness or depth 241 of FIGS. 1-3 and doped region62 is analogous in function to doped region 22 of FIGS. 1-3. Structure616 results.

Referring now to manufacturing stage 517 of FIG. 17, sidewall protector70 is removed. Structure 617 results. With respect to subsequentmanufacturing stages, other than out-diffusion effects that can be moresignificant in the manufacturing sequence illustrated by FIGS. 4-13,structure 617 of FIG. 17 is substantially equivalent to structure 605 ofFIG. 5. That is, cavity 50 has been formed in substrate 21 and theimpurities leading to doped regions 24, 64 and 22, 62 have been providedin the desire relationship to sidewall 27. In the manufacturing sequenceof FIGS. 4-13, regions 22, 24 are provided by direct doping of substrate21 (e.g., by ion implantation), and in the manufacturing sequence ofFIGS. 14-18 analogous regions 62, 64 are provided by excavation ofsubstrate 21 and epitaxial re-growth (with concurrent or subsequentdoping) in substantially the same locations relative to sidewall 27.

Referring now to manufacturing stage 518 of FIG. 18, persons of skill inthe art will understand that manufacturing stage 518 of FIG. 18 includesthe equivalent of manufacturing stages 506-513 wherein gate dielectricregion 26, gate conductor 28, central dielectric region 33, metal-SCalloy contact region 63 (equivalent to region 23), metal-SC alloycontact region 65 (equivalent to region 25), interlayer dielectric 34and connection 44, 48, and 42 are provided. Accordingly, the discussionof such manufacturing stages is incorporated here by reference.Structure 618 results wherein channel length 30 is determinedsubstantially by the combination of cavity etch depth 51 and depth 641of epi region 64 (analogous to depth 241 of doped region 24). When gate28 is appropriately biased, induced channel 29 forms between portion 622of doped region 62 and portion 642 of doped region 64.

Manufacturing sequence 514-518 and structure 618 have several advantagesrelative to manufacturing sequence 504-513 and structure 613. First theuse of epitaxial growth for forming doped regions 64, 62 permits moreabrupt junctions to be formed as compared to doped region 24, 22. Thisis useful in optimizing device design under certain circumstances.Second, doped regions 64, 62 may be formed of other materials thanmerely the material of substrate 21. For example, when substrate 21 isof silicon, rather than forming doped regions 64, 62 of epitaxialsilicon, in other embodiments such regions may be formed from straininducing semiconductor materials, i.e., SC materials having differentlattice constants than substrate 21. Non-limiting examples of suitablestrain inducing materials for use with silicon substrates are SiGe foruse in PMOS devices and/or SiC for use in NMOS devices. Other straininducing materials may also be used. The germanium concentration in SiGecan be varied from 20% to 50% and the carbon concentration in SiC can bevaried from 1% to 3% or more, but other concentrations may also be used.When regions 64, 62 are formed from such materials, strain is induced inthe region where conductive channel 29 is induced during operation ofdevice 80. Such strain is known to increase carrier mobility, therebyreducing the ON-resistance of the device having the strained channelregion. This permits non-planar devices of further improved propertiesto be provided and is a significant advantage.

FIGS. 19-27 show simplified cross-sectional views of MOSFET 80′ of FIGS.1-2 during various stages 519-527 of manufacture, according to still yetfurther embodiments of the invention. Persons of skill in the art willunderstand that these same manufacturing stages apply to the structureshown in FIG. 3 taking into account the differences in lateral sizes andlocations of the various regions being formed. Referring now tomanufacturing stage 519 of FIG. 19, manufacturing stage 519 follows fromstructure 614 of FIG. 14, and the discussion thereof is incorporatedherein by reference. Manufacturing stage 519 is desirable but notessential. In manufacturing stage 519, Implant B is applied to formdoped region 68 of depth 681. For convenience of processing, dopedregion 66 of depth 661 is formed at the same time, but is not essentialand does no harm. In other embodiments, it may be omitted. In general,implant B is provided so that depth 681 is greater than depth 641 ofsubsequently formed doped region 64 (e.g., see FIG. 18 or 27). Itspurpose is to provide a more graded junction than might otherwise beobtained merely with doped region 64 alone. This is useful in optimizingthe electrical properties of resulting MOSFET 80′. The energy of ImplantB should be adjusted so that depth 681 is approximately about 20 percentgreater than depth 641 of subsequently formed doped region 64. Implant Bis of the same conductivity type (and generally similar dopants) as thedoping of region 64 and desirably has a doping concentration in therange of about 2E18 to 1E19 cm⁻³, but higher and lower concentrationsmay also be used. Stated another way, the doping of region 68 beneathregion 64 is desirably of lower concentration than the doping of region64 by a factor of about 10 to 20, but other doping ratios may also beused. For manufacturing convenience, region 68 is shown in FIGS. 19-28as having the same lateral extent as doped region 64, but this is notnecessary and in other embodiments, region 68 may be localized to besubstantially adjacent to sidewall 27 where induced channel 29illustrated in FIG. 27 forms. Either arrangement is useful. Structure619 results.

Referring now to manufacturing stages 520 of FIGS. 20 and 521 of FIG.21, except for the presence of doped regions 68 and 66, thesemanufacturing stages are analogous to manufacturing stages 515 of FIG.15 and 516 of FIG. 16, and the discussion thereof is included herein byreference. Structure 621 results.

Referring now to manufacturing stage 522 of FIG. 22, sidewall protector70 is removed from structure 621 and layer 90′ is deposited over device80′. Layer 90′ is used to form a dummy gate, that is, a place-holder forgate 98 of FIGS. 26-27, analogous to gate 28 described previously. Thematerial of layer 90′ does not remain in the final structure of MOSFET80′ and performs no electrical function. Accordingly, any material thatis substantially differentially etchable with respect to substrate 21may be used for layer 90′. Silicon nitride, silicon oxide andcombinations thereof are non-limiting examples of suitable materials forlayer 90′, but other materials may also be used. It is desirable thatlayer 90′ is thick enough to substantially fill cavity 50 but thickerand thinner layers may also be used. Structure 622 results.

Referring now to manufacturing stage 523 of FIG. 23, structure 622 isplanarized (e.g., using CMP), masked (e.g., using photo-resist) andetched to provide central cavity 54′ approximately similar to cavity 54previously described (e.g., see FIG. 8) with adjacent dummy gate 90located against sidewall 27, i.e., in substantially the same location asoccupied by real gate 28 and associated gate dielectric 26 of FIGS. 1-2.Metal-SC alloy contact region 63 is formed in doped region 62 usingcavity 54′ and metal-SC alloy contact region 65 is formed in dopedregion 64, in substantially the same manner as previously described forcontact regions 23, 25 in connection with FIG. 9, the discussion ofwhich is incorporated herein by reference. Structure 623 results.Referring now to manufacturing stage 524 of FIG. 24, cavity 54′ isfilled with dielectric 33′ analogous to central dielectric region 33 andplanarized, as described for example in connection with FIGS. 10 and 11,the discussion of which is incorporated herein by reference. Centraldielectric region 33′ is approximately analogous to dielectric region 33of FIG. 11 but is laterally bounded by dummy gate 90 rather than gate28. Structure 624 results.

Referring now to manufacturing stage 525 of FIG. 25, structure 624 isetched to remove dummy gates 90, leaving substantially annular cavity 91is its place, in which sidewall 27 is exposed as is the portion of dopedregion 62 underlying cavity 91. Structure 625 results. Referring now tomanufacturing stage 526 of FIG. 26, cavity 91 has gate dielectric liner96 provided therein, covering sidewall 27 and the exposed portion ofunderling doped region 62 and contact region 63. Gate dielectric liner96 serves as the gate insulator of MOSFET 80′ and any material andthickness suitable for this purpose may be used for liner 96. Suchchoices are within the competence of those of skill kin the art. Siliconoxide, silicon nitride and combinations thereof are non-limitingexamples of suitable materials for dielectric liner 96, but otherinsulating materials may also be used, including materials havingrelatively high dielectric constants, that is, dielectric constantsgreater than about 4. The remaining empty portion of cavity 91 is filledwith gate conductor 98 and planarized. Gate conductor 98 is functionallyanalogous to gate conductor 28 already described. However, unlike gateconductor 28, since gate conductor 98 is formed after many of the otherregions of device 80′ have already been formed, most of the hightemperature operations associated with forming device 80′ and metal-SCalloy regions 63, 65 have already been provided, so much grater freedomis available regarding the choice of conductor for gate 98. For exampleand not intended to be limiting, metals, semi-metals, semiconductors,doped-semiconductors, conductive mixtures, alloys and combinationsthereof are all useful. TiN is preferred. Structure 626 results.

Structure 626 may be used as is or provided with further overlyingdielectric layers and electrical contacts or interconnections, as iscommon in the art. Referring now to manufacturing stage 527, structure626 has dielectric layer 34 formed thereon, vias corresponding to thedesired locations of electrical connections 42, 48, 44 provided therein(and through dielectric region 33′ in the case of conductor 42), whichare then filled with electrical conductors to form electricalconnections to doped (source or drain) region 62, gate 98 and doped(drain or source) region 64, respectively. Structure 627 results whereinchannel length 30′ is determined substantially by the combination ofcavity etch depth 51 and epi-depth 641 (equivalent to doping-depth 241)of doped region 64 plus any further depth provided by underlying dopedregion 68. Induced channel 29′—will form when gate 28 is appropriatelybiased, as has been previously discussed. Further dielectric layers andinterconnections may also be provided depending upon the particulardevice structure or integrated circuit being formed.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention, it being understood that various changes may be made in thefunction and arrangement of elements described and methods ofpreparation in an exemplary embodiment without departing from the scopeof the invention as set forth in the appended claims and their legalequivalents.

What is claimed is:
 1. A non-planar field effect transistor (FET),comprising: a semiconductor substrate of a first conductivity type andhaving a first surface; a first doped region of a second, opposite,conductivity type located adjacent the first surface, adapted to act asa source or drain, and extending to a first depth beneath the firstsurface; a second doped region of the second conductivity type, adaptedto act as a drain or a source, located in the substrate at a seconddepth beneath the first surface greater than the first depth and coupledto the first doped region by an interior sidewall of the substrate; agate conductor adjacent the interior sidewall of the substrate butseparated from the sidewall by a gate insulator, and adapted whenappropriately biased to form a conductive channel adjacent the sidewall;and a first electrical connection coupled to the second doped region, asecond electrical connection coupled to the first doped region and athird electrical connection coupled to the gate conductor, wherein thefirst, second and third electrical connections extend to the firstsurface.
 2. The FET of claim 1, wherein the interior sidewall isoriented at an angle α with respect to the first surface with a at leastabout 90 degrees.
 3. The FET of claim 2, wherein the interior sidewallis oriented at an angle α with respect to the first surface, wherein ais at least about 95 degrees.
 4. The FET of claim 1, wherein gateconductor has a substantially annular plan view shape.
 5. The FET ofclaim 4, wherein gate conductor has a substantially hollow annular planview shape with a central dielectric region and the first electricalconnection is located laterally within the central dielectric region. 6.A method of forming a non-planar field effect transistor (FET),comprising: providing a substrate having a first surface; forming acavity extending into the substrate a first distance to a bottomthereof, and with a sidewall extending between the bottom and the firstsurface; forming a first doped region in the substrate proximate thefirst surface and laterally adjacent to the sidewall; forming a seconddoped region in the substrate proximate the bottom of the cavity andextending laterally within the sidewall; forming a gate insulator on thesidewall; forming a gate conductor in contact with the gate insulatorand overlying the second doped region; and forming first, second andthird electrical connections, respectively, to the first doped region,the second doped region and the gate conductor, extending to the firstsurface.
 7. The method of claim 6, wherein the first and second dopedregions are formed substantially at the same time.
 8. The method ofclaim 7, wherein the first and second doped regions are formedsubstantially by doping the substrate.
 9. The method of claim 7, whereinthe first and second doped regions are formed substantially by etchingaway a first portion of the substrate adjacent the first surface andetching away a second portion of the substrate adjacent the bottom andepitaxially refilling the first and second portions of the substrate toform therein the first doped region and the second doped region,respectively.
 10. The method of claim 9, wherein epitaxially refillingcomprises epitaxially refilling with substantially the samesemiconductor material as the substrate.
 11. The method of claim 9,wherein epitaxially refilling comprises epitaxially refilling withsemiconductor material having a lattice constant different than alattice constant of the substrate.
 12. The method of claim 6, furthercomprising, forming first and second metal-semiconductor alloy contactregions, respectively in Ohmic contact with the first and second dopedregions.
 13. The method of claim 12, wherein forming the first dopedregion and the first contact region comprise forming them withsubstantially coincident lateral areas.
 14. The method of claim 13,wherein forming the second doped region and the second contact regioncomprise forming them with substantially unequal lateral areas.
 15. Themethod of claim 12, wherein the gate dielectric is formed after thefirst contact region.
 16. A method for forming a non-planar field effecttransistor (FET), comprising: providing a semiconductor (SC) substrateof a first conductivity type and having a first surface; forming acavity in the substrate having a bottom at a first depth from the firstsurface and a sidewall extending therebetween; forming a protectiveliner on the sidewall; excavating a first part of the substrateproximate the surface of the substrate laterally outside of thesidewall; isotropically excavating a second part of the substrateproximate the bottom and extending laterally to or beyond the sidewall;epitaxially refilling the first part of the substrate to a first depthto form a first region of a second, opposite, conductivity typeproximate the first surface of the substrate adjacent the sidewall;epitaxially refilling the second part of the substrate to form a secondregion of the second conductivity type proximate the bottom andextending to or beyond the sidewall; forming a gate insulator on thesidewall; and forming a gate conductor on the gate insulator oppositethe sidewall and overlying a part of the second region.
 17. The methodof claim 16, further comprising, providing a first connection coupled tothe first region and a second connection coupled to the second regionand a third connection coupled to the gate conductor, the first, secondand third connections extending at least to the first surface.
 18. Themethod of claim 16, wherein epitaxially refilling comprises epitaxiallyrefilling with one or more strain inducing materials having one or moredifferent lattice constants different than the substrate.
 19. The methodof claim 16, wherein forming the gate conductor comprises: forming adummy gate laterally in contact with the sidewall; removing the dummygate; forming the gate insulator in contact with the sidewall; andforming the gate conductor in contact with the gate insulator.
 20. Themethod of claim 16, wherein forming the gate conductor comprises:forming a dummy gate laterally in contact with the sidewall; forming adielectric region laterally adjacent the dummy gate; creating a voidbetween the sidewall and the dielectric region by removing the dummygate; providing the gate insulator on the sidewall and a portion of thesecond region underlying the void; and forming the gate conductor in aremaining portion of the void at least in contact with the gateinsulator.